Electric installation for rectifying alternating currents



March 24, 1936.

J. G. -w. MULDER ELECTRIC INSTALLATION FOR RECTIFYING ALTERNATING CURRENTS Filed April 17, 1930 Patented Mar. 24, 1936 UNITED STATES PATENT OFFIQE Johannes Gijsbertus Wilhelm Mulder, Eindhoven, Netherlands, assignor to N. V. Philips Gloeilampeniabrieken, Eindhoven, Netherlands Application April 17, 1930, Serial No. 445,190 In the Netherlands June 15, 1929 7 Claims.

The invention relates to an electric installation for rectifying alternating currents, which is particularly suitable for use for very high tensions and which comprises an incandescent cathode discharge tube.

When, for the rectification of currents at a tension up to several ten thousands of volts, use is made of incandescent cathode discharge tubes, such tubes have, as a rule, so high a vacuum 0 that the discharge current of the tube is a pure electron current and that no ionization occurs. The intensity of the current which such a discharge tube can pass is only small while these tubes have a high voltage drop and consequently afford a poor efficiency.

In this respect discharge tubes operating with gas ionization are more advantageous because they are capable of allowing very great current intensities to pass and operate with a low voltage drop. In general, however, such tubes are not suitable for operation at very high tensions, for example, at tensions of about 10,000 volts. In fact, it is essential that with increasing tube voltages, the gas pressure be lowered. A low gas pressure, however, causes a rapid disintegration of the incandescent cathode and consequently a short life of the tube while, in addition, a prolonged use isrendered impossible by the reduction of the gas pressure, which at such low pressures has a great influence. For this reason at tensions above 1000 volts one has only proceeded with hesitance in the use of gas-filled rectifiers.

In the installation according to the invention all the said disadvantages have been obviated. The installation comprises a discharge device, in which the incandescent cathode (preferably an oxide cathode) and one or more anodes are located in separate chambers which communicate with one another while in the chamber containing the incandescent cathode a pressure is maintained which is higher than that in the chamber containing the anode or anodes. The communication between the said separate chambers may conveniently be established by a channel of great circulation resistance.

, The difference in pressure in the various electrode chambers may be brought about by causing a substance to evaporate in the cathode chamber or in a vessel connected thereto, this vapour being condensed again in the. anode chamber which, if desired, is artificially cooled. This substance is preferably constituted by mercury. The dimensions of the discharge device may be chosen so small that by the discharge itself sufficient heat for the evaporation is developed. If desired, the

rise of temperature may be limited in this case by means of a cooling device. It is advisable, however, to give the device larger dimensions and to effectuate the evaporation with the aid of a special heating device, for example with an electric heating apparatus. This device may be located outside or within the exhausted chamber.

In order to effectuate or to facilitate the condensation of the vapour in the anode chamber, the installation according to the invention may 0 comprise a device whereby a blast of air is conducted along the anode chamber.

The condensed mercury may be used anew for the evaporation in the cathode chamber. For this purpose, the arrangement may be such that 15 mercury condensing in the colder parts is enabled to flow back from these parts to the evaporation chamber. This fiowing back occurs through the channels through which the discharge passes. Alternatively, however, there may 20 also be provided separate tubes which enable the mercury to flow back.

The vapour produced in the discharge device of the installation according to the invention usually sufiices to carry the discharge. The dis- 25 charge device may consequently be substantially free from other gases. In order to ensure a quiet operation, the wall of the device may be provided with conducting members which are electrically connected to the anodes and which extend to- 30 wards the cathode chamber. These members may be constituted by metal wires, for example of nickel, which are wound around the channel leading to the cathode chamber.

Outside the discharge tube and between the 35 anode chamber or chambers and the chamber containing the cathode may be arranged a screen destined to avoid transfer of heat between these chambers. If there are a plurality of anode chambers, they may surround the cathode cham- 4.0 ber which is surrounded by a screen.

In order that the invention may be clearly understood and readily carried into effect, it will be more fully described with reference to the accompanying drawing which represents diagram- 45 matically part of an electric installation according to the invention.

Referring to the drawing, 5 denotes an electric discharge device consisting of a plurality of chambers which communicate with each other. 50 The chamber 2 contains an incandescent cathode 3, preferably an oxide cathode. In a second chamber 4 is arranged an anode 5, graphite being particularly suitable as the material of the latter. In addition to the anode chamber shown 55 in the drawing, there may be provided a plurality of such chambers which each contain an anode, in which case rectification of alternating currents of two, three or more phases is possible. The anode chamber communicates with the cathode chamber 2 by means of a channel 6 which slopes downwards to the chamber 2. If the discharge device is designed for the rectification of a polyphase alternating current, it is important that the discharge channels which connect the chambers with the cathode chamber, are of equal length.

The anode 5 is connected to one of the ends of a transformer winding i whose other end, which, in the case of polyphase rectification, is the star point of a polyphase winding, constitutes the negative pole of the installation. The positive pole is constituted by the midpoint of an auxiliary winding 8 which supplies the heatingcurrent for the incandescent cathode. The primary transformer winding is not represented in the drawing.

A vessel 9 containing some liquid mercury, is in open communication with the cathode chamher 2. This vessel is surrounded by an electric heating element It? with the aid of which the mercury is heated owing to which the chamber 2 is filled with mercury vapour of such pressure that during operation no harmful disintegration of the incandescent cathode occurs. The discharge device is exhausted to a very high extent so that, with the'exception of mercury vapour, substantially no other gases are present.

Below the anode chamber 4 is arranged a ventilator H which is driven by an electric motor l2 and which causes a current of air to pass along the wall of the tube in order to cool the anode chamber, which is conducive to the-condensation of the mercury vapour contained in this chamber. As shown in the drawing the condensed vapour deposits on the wall in the form of drops which, accumulated to larger quantities, flow back to the vessel 9 through the tube 6 which slopes downwards to the cathode chamber. There is consequently a continuous circulation of mercury which evaporates from the vessel 9 and condenses in the anode chambers from which it returns as a liquid to the vessel 9. Due to the cooling the pressure of the mercury vapour in the anode chamber is very low and is only a fraction of one millimeter of mercury. The mercury contained in the vessel 9 is heated, however, to a temperature which causes the vapour pressure in the chamber 2 to rise to some millimeters of mercury. Suitable temperatures are those between about and C.

As far as that part of the discharge path which extends from the anode to the cathode chamber is concerned, the rectifier device thus has the character of a rectifier with very low gas pressure, owing to which it is suitable for very high tensions. During the inactive halfperiod the tension between the electrodes may therefore without any objection amount to 10 kv. and higher.

Inthe space around the incandescent cathode, however, there exists a high pressure such as occurs in gas filled rectifiers for low tensions.

Owing to this high pressure, positive ions impinging on the incandescent cathode have only a low speed which from the standpoint of the disintegration of the incandescent cathode is a very favourable circumstance, whereby a very suitable length of life is thus ensured. The high pressure has also a favourable efiect with respect 7 main discharge.

to the cathode drop. The above-described device permits the rectification of currents having an intensity of several amperes.

In the vicinity of the incandescent cathode is arranged an auxiliary electrode E3 which may be given a tension relative to the incandescent cathode, owing to which an auxiliary discharge is established which facilitates the production of the Conveniently, a source of direct current should be used for this purpose. The drawing represents a separate rectifier 5 ti for supplying a positive tension produced by full-wave rectification. The primary Winding of the transformer which feeds this rectifier is not illustrated. The winding 95, which is connected through resistances it to anodes H and whose mid-point is connected to the mid-point of the winding 8, may be provided, if desired, on the main transformer. The incandescent cathode !8 of the auxiliary rectifier is fed by an auxiliary winding l9 whose mid-point is connected to'the auxiliary electrode IS.

A screen 20 of metal or, preferably, of a substance which poorly conducts heat, such as asbestos or the like, is arranged between the anode and the cathode chambers, and has for its purpose to prevent thansfer of heat between the said chambers.

In order to prevent undesirable phenomena in the case of disturbances in the cooling of the anode chambers or in the heating of the mercury, there may be provided protecting devices, adapted, for example, to react on the temperature or on the pressure of the cooling air supplied'by the ventilator, and actuating relays whereby the current supply to the rectifier device is broken.

What I claim is:

1. A rectifier tube comprising an incandescible cathode and at least one anode and an envelope for said tube forming a chamber around said cathode and forming a chamber around said anode, said second chamber being connected with said first'chamber, a mercury vapor filling in said chambers, the pressure of the vapor in the cathode chamber being substantially greater than 1 millimeter of mercury and the pressure in said anode chamber being substantially less than 1 millimeter of mercury.

2. A rectifier tube for voltages above 10,000 volts, comprising an incandescible cathode and at least one anode, an envelope for said tube comprising interconnecting chambers to receive said cathode and said anode respectively, and a gaseous filling having a pressure substantially greater than 1 millimeter of mercury in the cathode chamber and substantially less than 1 millimeter of mercury in the anode chamber.

3. An electric installation for rectifying alternating current, comprising a discharge tube operating with an arc discharge, said tube having an envelope formed of a plurality of interconnected chambers, an ionizable vapor filling within said envelope, an anode in one of said chambers, an incandescible cathode in another of said chambers, and a liquid vaporizable to form said vapor filling and disposed substantially in said cathode chamber, and means to produce in said cathode chamber a substantially higher temperature and higher vapor pressure than in said anode chamber, said means comprising means for heating the cathode portion of the tube, and means for cooling other portions of the tube.

4. An electric installation for rectifying alternating current comprising, a discharge tube operating with an arc discharge, said discharge tube having an envelope formed of two chambers and a tube connecting said chambers, said connecting tube having an internal diameter less than one-fifth of its length and a cross-sectional area less than that of either chamber, an ionizable vapor filling within said envelope, an anode in one of said chambers, an incandescible cathode in the other chamber, and a liquid vaporizable to form said vapor filling and disposed substantially in said cathode chamber, and means for producing and maintaining in said cathode chamber a higher pressure and a higher temperature than in said anode chamber, said means comprising said connecting tube, means for heating said cathode chamber, and means for maintaining said anode chamber at a temperature lower than that of the cathode chamber.

5. An electric installation for rectifying alternating current comprising, a discharge tube operating with an arc discharge, said tube having an envelope formed of two interconnected chambers, an ionizable vapor filling within said envelope, an anode in one of said chambers, an incandescible cathode in the other chamber, and a liquid vaporizable to form said vapor filling and disposed substantially in said cathode chamher, a heating resistance for heating said liquid, and a device for circulating a current of cooling air along the anode chamber.

6. An electric installation for rectifying alternating current comprising, a discharge tube operating with an arc discharge, said tube having an envelope formed of two interconnected chambers, an ionizable vapor filling within said envelope, an anode in one of said chambers, an incandescible cathode in the other chamber, and a liquid vaporizable to form said vapor filling and disposed substantially in said cathode chamber, cooling means between said cathode chamber and said anode to condense the vapor, and a screen disposed between the cathode chamber and the cooled parts of the tube to prevent cooling of the cathode chamber.

'7. An electric installation for rectifying alternating current comprising, a discharge tube operating with an arc discharge and having an envelope formed of two interconnected chambers, an ionizable vapor filling Within said envelope, an anode in one of said chambers, an incandescible cathode in the other chamber, and a liquid vaporizable to form said vapor filling and disposed sub'stantially in said cathode chamber, a device for circulating cooling air to cool said anode chamber, and a screen mounted outside said tube and between said chambers to prevent the cooling of said cathode chamber.

J OHAN N ES GIJSBERTUS WILHELM MULDER. 

